By Lina carolina 
When the Kīlauea Volcano on Hawaiʻi Island unleashed its monumental eruption in May 2018, it not only reshaped the landscape of the Big Island but also sent an unprecedented plume of ash soaring nearly five miles into the atmosphere. This volcanic detritus, carried by prevailing winds across thousands of miles, has now been definitively linked to a rare and colossal summertime phytoplankton bloom in the North Pacific Subtropical Gyre. The groundbreaking findings, published in the recent issue of JGR Oceans, highlight a significant, and previously underappreciated, connection between terrestrial volcanic activity and the health of distant marine ecosystems, offering critical insights into oceanographic processes and the global carbon cycle.
The Scale of the Bloom: An Unprecedented Marine Event
The magnitude of the phytoplankton bloom was extraordinary, prompting researchers to describe it as "massive" and potentially the "largest ever reported for the North Pacific." David Karl, a co-author of the study and Professor at the University of Hawaiʻi (UH) at Mānoa’s Center for Microbial Oceanography: Research and Education, emphasized the sheer scale of the phenomenon. "The scale and duration of this bloom were both massive," Karl stated. "Our study shows the connection between the eruption of Kīlauea and bloom formation far from the volcano. This can be used to refine our understanding of phytoplankton bloom dynamics and to improve our understanding of the ocean’s carbon cycle."
This exceptional bloom, detected approximately 1,200 miles west of the Kīlauea volcano, underscores the far-reaching impacts of volcanic events. While Kīlauea is renowned for its frequent eruptions, with multiple occurrences over the past four decades, this specific instance marks the first documented link between its ashfall and a significant open-ocean phytoplankton bloom. The 2018 eruption was not merely another event; it stood out as one of Kīlauea’s most substantial in over two centuries, spewing millions of cubic feet of molten lava into the ocean and releasing an estimated 50 kilotons of sulfur dioxide and 77 kilotons of carbon dioxide into the atmosphere daily.
A Cascade of Events: From Volcano to Ocean
The journey of volcanic ash from Kīlauea to fostering life in the remote North Pacific is a complex yet elegant chain of natural processes. Previous research, also spearheaded by UH Mānoa oceanographers, had already identified a localized phenomenon: as lava flowed into the ocean, it stirred and warmed nutrient-rich bottom waters. This upwelling of vital nutrients to the sunlit surface stimulated phytoplankton growth in the immediate vicinity of Hawaiʻi Island, creating a visible plume of microbial life.
However, the 2018 eruption’s sheer power injected volcanic materials, including ash, much higher into the atmosphere, where they could be transported over vast distances by prevailing winds. Wee Cheah, the study’s corresponding author and Senior Lecturer at Universiti Malaya’s Institute of Ocean and Earth Sciences, explained the atmospheric transport mechanism. "After the 2018 eruption, the prevailing winds transported ash particles to the west," Cheah noted. "The trajectories of the ash were recorded by Earth-orbiting satellites that detect changes in the optical clarity of the atmosphere, the so-called aerosol optical depth. Depending on the density, size, and shape of the particulate matter and local atmospheric conditions, especially rainfall, the ash eventually falls out of the atmosphere and into the surface ocean."
The research team, led by Chun Hoe Chow, Associate Professor at the National Taiwan Ocean University’s Department of Marine Environmental Informatics, meticulously analyzed satellite data. This analysis involved not only tracking the atmospheric dispersal of ash but also monitoring ocean color. Ocean color is an indirect indicator of phytoplankton abundance, as these microscopic organisms contain chlorophyll, which reflects sunlight in characteristic ways. The satellite imagery revealed a massive bloom concentrated near the dateline, a region typically characterized by nutrient-poor waters.
The Crucial Role of Volcanic Nutrients
The open ocean, particularly the North Pacific Subtropical Gyre, is known for its oligotrophic conditions – meaning it has very low concentrations of essential nutrients. This scarcity of nutrients typically limits phytoplankton growth. However, volcanic ash is not just inert rock dust; it is a rich source of minerals, particularly iron.
"The waters in the open ocean of the Pacific are nutrient depleted and the addition of volcanic ash, especially iron in the ash, and to a lesser extent other trace elements and possibly phosphate, can stimulate the growth of marine phytoplankton," explained Professor Karl. He further elaborated on the specific types of phytoplankton that benefited: "especially the so-called nitrogen-fixing microbes that can growth in the absence of additional nitrogen." These specialized microbes are capable of converting atmospheric nitrogen into a usable form, further fueling their growth in otherwise nutrient-limited environments. The presence of these essential trace elements in the ash provided the critical spark needed to ignite a substantial bloom in a region where such an event would normally be highly unlikely.
A Carbon Cycle Conundrum: Sequestration and Release
The dramatic proliferation of phytoplankton has profound implications for the ocean’s carbon cycle. Phytoplankton play a vital role in absorbing atmospheric carbon dioxide through photosynthesis. When these microscopic organisms thrive and multiply, they create a significant amount of organic matter. As the bloom eventually subsides, these organisms die and sink to the deep ocean. This process, known as carbon export, effectively removes organic carbon from the surface layer of the ocean and, consequently, from the atmosphere.
The researchers’ estimates suggest that the amount of organic carbon exported from the surface during this bloom could be substantial, potentially equivalent to about half of the carbon dioxide initially released by the Kīlauea eruption. "Our estimates are that export of organic carbon may be equivalent to about half of the carbon dioxide initially released from the eruption," Karl stated. This natural sequestration process, where carbon is drawn down into the ocean depths, is a crucial component of Earth’s climate regulation.
This finding suggests that volcanic eruptions, while releasing greenhouse gases, can also trigger natural mechanisms that mitigate their impact. "This marine carbon dioxide sequestration is a natural process that probably occurs whenever volcanic eruptions inject ash into the atmosphere and carry that particulate matter out to sea," Karl elaborated. "The combination of ash deposition and the nutrient-starved conditions in our study area aligned to create a massive bloom that was easily seen by satellite remote sensing and Argo floats that had been previously deployed in that region."
Timeline of the 2018 Kīlauea Eruption and Subsequent Bloom:
- May 3, 2018: The Kīlauea volcano begins its major eruptive phase, characterized by fountaining lava, gas emissions, and the formation of a significant ash plume that reaches high into the atmosphere.
- May to August 2018: Prevailing winds transport volcanic ash westward across the Pacific Ocean. Satellite data begins to detect anomalies in atmospheric optical depth, indicating the presence of ash particles.
- June – August 2018: Satellite ocean color sensors detect a large, unusual phytoplankton bloom forming in the North Pacific Subtropical Gyre, approximately 1,200 miles west of Hawaiʻi.
- Post-Bloom Analysis: An international team of researchers, utilizing satellite data, atmospheric trajectory models, and oceanographic datasets, connects the observed phytoplankton bloom directly to the ashfall from the Kīlauea eruption.
- Recent Publication: The findings are published in JGR Oceans, detailing the scientific evidence for the link between volcanic ash and the massive marine bloom.
Broader Implications and Future Research
The study’s implications extend beyond understanding a single event. It provides a critical case study for refining models of phytoplankton bloom dynamics, particularly in nutrient-limited oceanic regions. Furthermore, it enhances our understanding of the ocean’s role in the global carbon cycle, highlighting the potential for volcanic activity to influence carbon sequestration rates.
The research team is already looking ahead. The ability to predict and monitor such events has significant scientific and environmental value. If another major volcanic eruption occurs with the potential to inject significant ash into the atmosphere, the researchers are prepared to deploy a research vessel. This would allow for real-time observation and sampling of the bloom’s development and response, providing invaluable data for future studies.
The connection between volcanic activity on land and the vast, often invisible, life supported by the ocean’s surface serves as a potent reminder of the interconnectedness of Earth’s systems. The 2018 Kīlauea eruption, a spectacle of terrestrial power, ultimately fueled a bloom of microscopic life that quietly played a significant role in the planet’s ongoing carbon balance. This research not only illuminates a fascinating natural phenomenon but also underscores the importance of continued scientific observation and international collaboration in unraveling the complexities of our planet.
